Process for microencapsulation

ABSTRACT

A process for encapsulating a wide variety of target materials, including both hydrophilic and hydrophobic materials, employs condensation of two reactive compounds to form shells around core phase particles including target material dispersed in a continuous phase. One of the reactive compounds has at least two active methylene functional groups per molecule, the other being an active methylene-reactive crosslinking agent. Either type of the reactive compounds can be dispersed in the continuous phase, the other being dispersible in the core phase. Applications include controlled release microencapsulation of agriculture chemicals and biocides.

This application is a continuation of application Ser. No. 89,694, filedAug. 26, 1987 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing microcapsulescontaining a target material, the microcapsules produced thereby, andcompositions containing these microcapsules. More particularly, thepresent invention relates to a polymerization process formicroencapsulation.

2. Brief Description of the Prior Art

A variety of methods for the preparation of microcapsules are known. Ingeneral, as an initial step one fluid is dispersed within another, thetwo fluids being immiscible, or nearly so, and in any case formingseparate phases. A common example is the oil-in-water (o/w) dispersion,although water-in-oil (w/o) dispersions are also well known, and theonly physical criterion for selecting the fluid pair is mutualincompatibility at the selected temperature and pressure. Often asurface-active dispersant or protective colloid, such as polyvinylalcohol in the case of oil-in-water dispersions, is dispersed ordissolved in the continuous phase to stabilize the dispersion. Theultimate object is to form a capsular wall or shell around the dispersedphase droplets or particles, the dispersed phase being formed by orcontaining a target material which is to be encapsulated.Microencapsulation techniques are reviewed in I. E. Vandergaer,Microencapsulation (Plenum Press, London 1974). The methods for formingthe wall can be broadly divided into physical and chemical techniques.

The physical technique, complex coacervation, involves precipitation ofa polymeric species at the interface between the continuous anddiscontinuous phase. For example, gelatin, dissolved or dispersed in acontinuous aqueous phase at controlled temperature and pH, can becoacervated or precipitated at the interphase between the aqueous phaseand a dispersed organic fluid phase, by reaction with an anionicallycharged colloid, such as gum arabic, vinyl acetate-maleic anhydridecopolymer, sodium alginate, polyacrylic acid, or the like. The walls orshells formed at the interface can be subsequently hardened by physicalor chemical treatment, such as disclosed in U.S. Pat. No. 2,800,457.Coacervation processes typically require careful control over processconditions such as reactant concentrations, temperature, and pH, andemploy substantial proportions of a relatively expensive material,gelatin, in forming the capsule shells. The processes are complex, andgive microcapsules which typically have poor water resistance.

Numerous chemical techniques for forming the microcapsule shells havealso been proposed. For example, urea and formaldehyde or aurea-formaldehyde precondensate can be dispersed in a continuous aqueousphase, and subsequently induced to react to give a urea-formaldehydecondensate which forms encapsulating shells around a dispersed phasecontaining the target material. Urea-formaldehyde microencapsulation istaught, for example, in U.S. Pat. Nos. 3,016,309 and 3,796,669. The useof polymeric species such as gum arabic, polyacrylic acid, alkylacrylate-acrylic acid copolymers, and hydrolyzed poly(ethylene-co-maleicanhydride) to modify the properties of urea-formaldehyde shells isreviewed in U.S. Pat. No. 4,552,811. Processes in which the microcapsuleshell polymer is polymerized in either the continuous phase or thediscontinuous phase are often referred to as "in-situ" techniques.

The in-situ shell-forming materials can be included in the discontinuousphase. For example, U.S. Pat. No. 4,626,471 discloses in-situpolymerization of certain multifunctional epoxy resins using polyaminecuring agents. The epoxy resin and amine are emulsified in aqueoussolution, and the temperature is elevated to promote cure of the resin.The cured resin migrates to the interface to form the shells of themicrocapsules.

Another set of methods for encapsulating target materials involvesinterfacial polymerization, the polymeric shell being polymerized at ornear the interface between the continuous and discontinuous phases.Typically, the polymerization reaction is a condensation or additionreaction involving two types of difunctional monomer, the first beingdissolved or dispersed in the continuous phase, the second beingdissolved or dispersed in the discontinuous phase.

For example, U.S. Pat. No. 4,622,267 discloses an improved interfacialpolymerization technique for preparing microcapsules for carbonless copypaper. The target material (color-former) is initially dissolved in agood solvent and an aliphatic diisocyanate soluble in the goodsolvent/color former mixture is added. Subsequently, a poor solvent forthe aliphatic diisocyanate is added until the turbidity point is justbarely reached. This organic phase is then emulsified in an aqueoussolution, and a reactive amine is added to the aqueous phase. The aminediffuses to the interface, where it reacts with the diisocyanate to formpolymeric polyurethane shells. A similar technique, used to encapsulatesalts which are sparingly soluble in water in polyurethane shells, isdisclosed in U.S. Pat. No. 4,547,429.

An interfacial photopolymerization method is disclosed in U.S. Pat. No.4,532,183. In this addition polymerization technique, free radicalpolymerizable monomers are present in both a continuous aqueous phaseand a discontinuous oil phase. The aqueous phase can include ahydroxyalkyl acrylate or methacrylate while the oil phase can containcopolymerizable ethylenically unsaturated oil soluble monomer such as analkyl acrylate. Photoinitiator can be added to either phase, and apolyfunctional isocyanate prepolymer is preferably added to the oilphase to enhance shell formation.

Microcapsules have been used to encapsulate a great variety of targetmaterials. The most important commercial use of microencapsulatedmaterials has been in the manufacture of carbonless copy paper.Typically, a colorless dye precursor or color-former such as crystalviolet lactone is encapsulated in microcapsules having fairly rigidshells, and a slurry containing the microcapsules is coated onto theback of a first sheet (CB sheet). The face of a second sheet is coatedwith an acid, color developing material such as an acidic clay or aphenolic resin (CF sheet). The sheets are manufactured into a form withthe CB sheet over the CF sheet. Pressure on the CB sheet, such as thatgenerated by the ball of a ballpoint pen, ruptures the shells of themicrocapsules to free the dye-precursor to react with the colordeveloper and form a copy of the original on the CF sheet.

Other microencapsulated target materials have included agriculturalchemicals, food for newly hatched fish, pharmaceuticals, pesticides,flavorings, scents, adhesives, toners for xerography, fertilizers, inks,toxic salts and crosslinking agents and other reactive chemicals. Thenature of the application strongly influences the characteristics of thepolymeric shells. For example, in the case of encapsulatedpharmaceuticals, sustained, gradual release of the target material fromthe microcapsules may be desired, and the shell porosity and/orbiodegradability could be controlled to achieve the desired releasekinetics. In the case of carbonless copy paper, the microcapsules mustbe rigid for easy rupturability, and relatively impervious to diffusionby the color-former for stability.

Microencapsulation techniques are often directed to the problemsassociated with encapsulating specific target materials and cannot beeasily generalized to different types of target materials. For example,the in situ polymerization of urea-formaldehyde precondensates toencapsulate dispersed oil phase droplets containing color former cannotbe easily adapted to target materials requiring water-in-oilencapsulation, such as water-soluble vitamins. There is a need for anencapsulation process of sufficient breadth such that a wide variety oftarget materials can be successfully encapsulated. In particular, thereis a need for an encapsulation process which can be used to encapsulateboth hydrophilic target materials, such as water-soluble targetmaterials, and hydrophobic target materials, such as oil-soluble targetmaterials.

SUMMARY OF THE INVENTION

The present invention provides a process for microencapsulating a targetmaterial in a dispersion of insoluble coreshell particles which aredispersed in a continuous fluid phase. This process is applicable toencapsulating a wide variety of target materials, including bothhydrophobic and hydrophilic target materials. The process employs thepolymerization reaction of a first reactive compound with a secondreactive compound, one of these compounds being a compound having atleast two active methylene functional groups per molecule, the othercompound being a active methylene-reactive crosslinking agent.

The process comprises preparing a core emulsion including a core phaseof discrete core particles dispersed in the continuous fluid phase. Thecore emulsion is prepared by emulsifying a mixture comprising:

(1) a target material, and

(2) a dispersant for the core particles in the continuous phase.Preferably, the mixture also contains a first reactive compoundinsoluble in the continuous fluid phase, the first reactive compoundbeing selected from one of

(1) compounds having at least two active methylene functional groups permolecule, and

(2) active methylene-reactive crosslinking agents. However, the firstreactive compound can be added to the continuous phase after the coreemulsion has been prepared.

The process further includes combining with the continuous fluid phase asecond reactive compound soluble or dispersible in the continuous phaseand selected from one of

(1) compounds having at least two active methylene functional groups permolecule, and

(2) active methylene-reactive crosslinking agents, the first reactivecompound reacting with the second reactive compound to form polymericencapsulating shells around the cores.

In one embodiment of the process, the continuous fluid phase includeswater; for example, it can be an aqueous solution. In this embodimentthe core phase and the target material are hydrophobic, and the firstreactive compound is water-insoluble. The first reactive compound can beselected from water-insoluble compounds which have at least two activemethylene functional groups per molecule. If so, the second reactivecompound can be selected from water-soluble active methylene reactivecrosslinking agents.

The broad applicability and generality of the present process isapparent. Starting with a specific target compound, the choice of thefirst and second reactive compounds, as well as the character of thecontinuous and dispersed phases, can be selected to reflect the physicaland chemical properties of the target compound. Thus, a great variety oftarget materials can be microencapsulated using the process of thepresent invention.

The microcapsules produced by the present process can be seperated fromthe continuous phase if desired. The microcapsules containing the targetmaterial can be adapted to either sudden release or sustained releaseapplications, such as carbonless copy paper and agricultural chemicalmicrocapsulation, respectively, by choice of first and second reactivematerials to give polymeric shells with appropriate physical properties.

Another advantage of the process of the present invention is that it canbe used to produce microcapsules having diameters on the order of 0.5micron and less, significantly less than the diameter of microcapsulesproduced using many common techniques.

DETAILED DESCRIPTION

The microencapsulation process of the present invention is applicable toa wide variety of target materials, including both hydrophilicmaterials, such as water-soluble pesticides, for example, ethylenebis-dithiocarbamate salt fungicides and Kathon® (trademark of Rohm andHaas Co.) biocide, and hydrophobic materials such as water-insolublepesticides, for example, Karathane® (trademark of Rohm and Haas Co.) andSkane® (trademark of Rohm and Haas Co.) M-8 mildicide. Other types oftarget materials which can be encapsulated using the present processinclude color-formers for carbonless copy paper, such as crystal violetlactone, benzoyl leuco methylene blue, the paratoluene sulfonate ofMichler's Hydrol, 3-diethylamine-6-methyl-7-anilinofluoran, and thelike. Reactive chemicals such as di- and poly- isocyanates, organicperoxides, and epoxy-functional compounds can also be encapsulated.Similarly, pharmaceuticals, scents, flavorings, xerographic toners,inks, catalysts, fertilizers, adhesives, inorganic salts,photosensitizers, photoactivators, reactive chemicals, and a greatvariety of other target materials can be microencapsulated using theprocess of the present invention. More than one target material can bemicroencapsulated simultaneously by the present process, as in the casewhere two target materials are mutually soluble.

When hydrophobic target materials are to be encapsulated, a hydrophiliccontinuous fluid phase, such as water or an aqueous or alcoholicsolution, is employed. The hydrophobic target material is dispersed inthe hydrophilic continuous phase, along with at least one hydrophobicfirst reactive compound. Conversely, when hydrophilic target materialsare to be encapsulated, a hydrophobic continuous phase, such as an oilor nonaqueous organic solvent, is employed. The hydrophilic targetmaterial is dispersed in the hydrophobic continuous phase, along with atleast one hydrophilic first reactive compound.

The first reactive compound can be initially mixed with the targetmaterial, and the mixture subsequently dispersed in the continuous fluidphase, or the first reactive compound can be mixed with the continuousphase after a core phase including the target material has been formed.If desired, a mixture of first reactive compounds can be used.

The use of "first" in "first reactive compound" denotes thecompatibility of the compound with the core phase, and is not intendedto indicate or suggest an order of addition. Similarly, the use of"second" in "second reactive compound" denotes the compatibility of thiscompound with the continuous phase, and does not relate to the order ofaddition.

The first reactive compound can be either a compound having at least twoactive methylene groups per molecule or a compound being an activemethylene-reactive crosslinking agent. The choice of either of these twotypes of compound for the first reactive compound fixes the character ofthe second reactive compound, in the sense that the second reactivecompound must be selected to be reactive with the first reactivecompound. Thus, if the first reactive compound is selected to be acompound having at least two active hydrogen functional groups permolecule, then the second reactive compound must be an activemethylene-reactive crosslinking agent. Conversely, should the firstreactive compound be selected to be a compound which is an activemethylene-reactive crosslinking agent, the second reactive compound mustbe a compound having at least two active hydrogen functional groups permolecule.

When a hydrophobic target material is to be encapsulated, then the firstreactive compound must be sufficiently hydrophobic so that it, alongwith the hydrophobic target material, form a separate, dispersed,noncontinuous phase within the hydrophilic continuous phase. Similarly,when a hydrophilic target compound is to be encapsulated, the firstreactive compound must be sufficiently hydrophilic so that it and thetarget-compound form a dispersed core phase within the hydrophobiccontinuous phase.

Preferably, the first reactive compound is substantially insoluble inthe continuous phase. However, first reactive compounds which areslightly or sparingly soluble in the first continuous phase can also beused in the present process. By "substantially insoluble" is meanthaving a solubility of less than about one percent by weight. Inaddition to its being substantially insoluble in the continuous phase,it is preferred that the first reactive compound be miscible with, orsoluble in, the target material, such that the core phase includes boththe target material and the first reactive compound. The polymericproduct of the first and second reactive compounds is preferablyinsoluble in both the continuous fluid phase and the dispersed corephase.

When a hydrophobic target material is to be encapsulated, it ispreferred that the core phase include an "emulsion stabilizer," such asdisclosed in U.S. Pat. Nos. 4,336,173 and 4,113,687 (Ugelstad). Theemulsion stabilizer is a hydrophobic organic compound which serves toincrease the stability of the dispersed core phase, encourages theformation of a fine dispersion of core particles having a narrowparticle size distribution, and discourages agglomeration of theindividual core particles into particles having dimensions larger thanthose desired. The choice of the emulsion stabilizer depends to someextent on the target material and the first reactive compound; theemulsion stabilizer is preferably selected to be miscible with both thetarget material and the first reactive compound. When the targetmaterial and the first reactive compound are not completely miscible orsoluble in one another, it may be possible to select an emulsionstabilizer in which both the target compound and the first reactivecompound are both soluble. Preferably, the emulsion stabilizer, thefirst reactive compound, and the target material form a ternarysolution, dispersed as the core phase in the hydrophilic continuousfluid phase.

Examples of emulsion stabilizers which can be used in the process of thepresent invention include the dialkyl phthalate esters, such as dibutylphthalate, dimethyl phthalate, and dioctyl phthalate; alkyl aralkylphthalates such as butyl benzyl phthalate; solvents for targetmaterials, including alkyl naphthalenes, phenylxylylethanes,alkylbiphenyls, polyhalogenated biphenyls, hydrogenated and partiallyhydrogenated terphenyls, paraffin oils, chlorinated paraffin oils,mineral oils, trichlorobenzene, nitrobenzene, tricresylphosphate, maleicacid alkyl esters, dibenzylbenzene, linear alkylbenzenes having about10-14 carbon atoms, polyarylmethanes, petroleum ethers; organic solventssuch as toluene, xylene, and the like; and mixtures thereof. The typeand quantity of emulsion stabilizer are selected with the understandingthat the emulsion stabilizer will be confined within the microcapsulesafter polymerization. Thus, emulsion stabilizers which tend toplasticize or dissolve the polymeric microcapsule shells are avoidedwhen rigid, easily rupturable shells are desired. Similarly, emulsionstabilizers which tend to react with the target material or reduce itsefficacy are to be avoided.

When the target material is hydrophobic, the first reactive compound canbe a hydrophobic compound having at least two active methylene groupsper molecule. Similarly, when the target compound is hydrophilic, thefirst reactive compound can be a hydrophilic compound having at leasttwo methylene groups per molecule.

By "active methylene" group is meant a methylene group having an active,or acidic, hydrogen atom, by virtue of the electron-withdrawing natureof functional groups proximate the active methylene group. Examples offunctional groups which contain active methylene groups includefunctional groups having the structural formula

    --X--C(O)--CH.sub.2 --Z,

the group X adjacent the carbonyl carbon being selected from --NR--,--O--, --S--, --O(CH₂ CH₂ O)_(m) [CH(CH₃)CH₂ O]_(n) --, and --N(CH₂ CH₂O)_(m) --[CH(CH₃)CH₂ O]_(n) --, where m, n=0-4, independently; and thegroup Z adjacent the methylene group being selected from --C(O)R, --CO₂H, --CO₂ R, --C(O)NHR, --C(O)NR₂, --CN, --NO₂, --SOR, --SO₂ R, --SO₃ R,phenyl, and (C₁ -C₃)alkyl-substituted phenyl; R being selected from (C₁-C₆)alkyl. Thus, such active methylene-containing functional groups as--O--C(0)--CH₂ --CO₂ H, --N(CH₃)--C(0)--CH₂ --CO₂ CH₃, --S--C(0)--Ch₂SO₃ C₂ H₅ and --O--C(0)--CH₂ --C(0)N(CH₃)₂ are included.

Examples of preferred active methylene functional groups include--NHC(O)CH₂ C(O)CH₃, --OC(O)CH₂ C(O)CH₃ (i.e. acetoacetyl), --NHC(O)CH₂CN, and --O--C(O)CH₂ CN (i.e. cyanoacetyl).

In general, the active methylene-containing compound can be prepared bythe condensation of a diol or polyol or diamine or polyamine with acompound having the structural formula

    H--X--C(O)--CH.sub.2 --Z

where X and Z are given above. Examples of diols and polyols which canbe used include diols, such as ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol; 1,2-propanediol,1,3-propanediol, dipropylene glycol, 2,2-dimethyl-1,3-propanediol,2,2,4-trimethyl-1,3,-pentanediol; di(hydroxyethyl)- anddi(hydroxypropyl)- adipate, azelate, dodecanoate, maleate and fumarate;1,3-butanediol, 1,4-butanediol, 2-buten-1,4-diol, 1,5-pentanediol,1,6-hexanediol; 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol; 1,2-cyclohexanediol, 1,3-cyclohexanediol,1,4-cyclohexanediol; 1,7-heptanediol, 1,8-octanediol,2-ethyl-1,3-hexanediol, 1,9-nonanediol, 1,10-decanediol,1,12-dodecaediol, 4,4'-isopropylidenediphenol and its ethoxylates orpropoxylates; 2,2'-thiodiethanol, 3,3'-thiodipropanol;N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine,N-phenyldiethanolamine; and N-methylol-, N-(2 -hydroxyethyl)-, andN-(2-hydroxypropyl)-derivatives of bisamides, ureas, and hydantoins-,and triols such as glycerol; 2-ethyl-2-(hydroxymethyl)-1,3-propanediol,1,1,1,-tris(hydroxymethy)-ethane, or their ethoxylates and propoxylates;triethanolamine; N-methylol-, N-(2-hydroxyethyl)-, orN-(2-hydroxypropyl)- derivatives of quanamines, melamine, and cyanuricacid; tetrols such as pentaerythritol; N-methylol-, N-(2-hydroxyethyl)-,or N-2(hydroxypropyl)- derivatives of guanamines, melamine, etc.; hexolssuch as dipentaerythritol, sorbitol; N-methylol-, N-(2-hydroxyethyl)- orN-(2-hydroxypropyl)- derivatives of melamine; and octols such astripentaerythritol.

Examples of hydroxy-functional compounds which can be used include lowmolecular weight hydroxy-functional polymers and oligomers, such asoligomers of hydroxyethyl acrylate and/or hydroxyethyl methacrylate andother hydroxyalkyl acrylates and methacrylates; polyvinylalcohols; andoligosaccharides. Such polymeric or oligomeric hydroxy-functionalcompounds would tend to form multi-functional active methylene compoundssuch as multi-functional aceto- or cyano-acetates.

When the first reactive compound is to be a hydrophobic active methylenecontaining compound, the diol or polyol and the group X and R areselected to confer appropriate hydrophobicity. Examples of hydrophobiccompounds having at least two active methylene groups per molecule andwhich can be used as hydrophobic first reactive compounds in the presentprocess include the tris(acetoacetyl)trimethylolpropane,tris(cyanoacetyl)trimethylolpropane,tris(nitroacetyl)trimethylolpropane,bis(N-methyl-N-hydroxyethylcyanoacetamido)adipate,bis(cyanoacetamido)ethoxyadipate,tris(isopropylinolocyanoacetyl)trimethylolpropane,tetra(acetoacetyl)pentaerythritol, tetra(acetoacetyl)erythritol,tris(cyanoacetyl)glycerol, tris(acetoacetamido)melamine,bis(isopropylidiocyanoacetyl)1,4-butylene glycol,bis(cyanoaceto)neopentyl glycol, and bis(acetoacetyl)diethylene glycol.

Mixtures of di- and/or poly-functional alcohols can be condensed with asingle active methylene compound, or mixtures of active methylenecompound can be condensed with a single di- and/or poly-functionalalcohol, or mixtures of di-and/or poly-functional alcohols and mixturesof active methylene compounds can be condensed, in order to preparecompounds having at least two active methylene groups per molecule foruse in the process of the present invention, and mixtures of suchcompounds can be used in the present process.

When the dispersed core phase is hydrophobic, the continuous fluid phaseis hydrophilic. Examples of hydrophilic continuous fluid phases whichcan be used in the process of the present invention include water,alcohols, and aqueous solutions, including alcoholic solutions andaqueous solutions of inorganic salts, e.g. MgNO₃, zinc acetate. Forexample, a saline solution containing from about 0 to 0.25 g NaCl per gof water can be used. Examples of alcohols which can be used includemethanol, ethanol, n-propanol, isopropanol, ethylene glycol, diethyleneglycol, glycerol, and mixtures thereof.

A hydrophilic continuous fluid phase can include dispersing agents forthe dispersed core phase. Examples of dispersing agents includepolymeric dispersants and protective colloids such as polyvinyl alcohol,polyvinyl acetate, gum arabic, carboxymethyl cellulose,hydroxyethylcellulose, partially hydrolyzed polyvinyl alcohol, andstyrene-maleic anhydride copolymers. The dispersing agents aid indispersing, setting the particle size and stabilizing the hydrophobiccore particles in the hydrophilic continuous phase, as well asmaintaining the colloidal stability of the final dispersion, and theiruse is well known in the art.

Conventional surface active agents, such as are known in theemulsification arts, can also be used to aid in dispersing andstabilizing the hydrophic core phase particles within the hydrophiliccontinuous phase. Examples of surface active agents which can be used todisperse and stabilize the hydrophobic core phase particles includedialkyl sulfosuccinates, such as diethylhexyl sulfosuccinate and othersurface active agents such as sodium lauryl sulfate, sodiumdodecylbenzene sulfonate; alkali metal salts ofalkylarylpolyethoxyethanol sulfates, sulfonates, or phosphates;stearyldimethylbenzylammonium chloride, etc.

The dispersion of the core phase in the continuous phase can beaccomplished by any technique known in the art. For example, a solutionincluding the target material and the compound containing at least twoactive methylene function groups can be added to the continuous phase.The target material containing solution can also contain an emulsionstabilizer if desired in the case of a hydrophobic solution. Thecontinuous fluid phase can be vigorously mixed as the target materialcontaining solution is gradually added, thus forming the dispersed coreparticles within the hydrophilic continuous phase. The mixing can beaccomplished by high speed stirring, such as is used in the interfacialpolymerization art, or in another conventional manner used in theemulsification art; such as ultrasonically, by shaking, or by employinga colloid mill or homogenizer.

The dispersion conditions, such as the shear rate and degree ofagitation, the temperature, and the volumetric ratio of the dispersedbase to continuous phase, can be adapted to give the core particle sizedesired. If high speed stirring is used, the present process permitscore particles, and consequently microcapsules having an averagediameter of about 0.2 micron and less can be prepared. Conversely, iflarger particle sizes are desired, by varying dispersion conditionmicrocapsules having an average diameter of about 100 microns andgreater can be prepared.

When the dispersed core particles contain a hydrophobic first reactivecompound containing at least two active methylene functional groups, thecapsule shells are formed by material which is polymerized from thehydrophobic first reactive compound and a hydrophilic second reactivecompound. The hydrophilic second reactive compound in this case is anactive methylene reactive crosslinking agent.

In general, the second reactive compound can be added to the continuousphase after the core phase has been dispersed therein. Alternatively,the second reactive compound can be included in the continuous phasebefore the core phase is dispersed, provided the core phase can bedispersed before substantial reaction between the first and secondreactive compound.

If desired, the target material initially can be dispersed in thecontinuous phase. The first reactive material can be added to the systemwith mixing, to permit the first reactive material to mix with thedispersed phase. Subsequently, the second reactive material can be addedto the system. The order of addition of the first and second reactivematerials can be reversed provided that the time constant for mixing isshort compared with the time constant for reactions between the firstand second reactive compounds or provided the reaction will besubsequently catalyzed, for example, by raising the pH of the system.

Examples of hydrophilic active methylene-reactive crosslinking agentswhich can be used include hydrophilic aldehydes, latent aldehydeshydrophilic bis(alkylidenes) of compounds containing at least two activemethylene groups, hydrophilic alpha, beta-ethylenically unsaturatedcarbonyl compounds, and hydrophilic hydrazones.

Examples of hydrophilic aldehydes which can be used includeformaldehyde, glyoxal, glutaraldehyde, furfural, acrolein, methacrolein,propionaldehyde, acetaldehyde and crotonaldehyde.

By latent aldehyde is meant a compound which will generate an aldehydein-situ in the reaction mixture under appropriate reaction conditions.Examples of latent aldehydes include: adducts of a bisulfite salt and analdehyde (having a functional group having the formula --C(OH)SO₃ ⁻ M⁺,where M is selected from the alkali metals); hemiacetals; acetals;adducts of an aldehyde and ammonia, such as hexamethyltetraamine,hexahydro-2,4,6-trimethyl-1,3,5-triazine, and aminals (compounds havinga functional group having the formula --C(OH)HNH₂ or --CH(NR₂)₂ where Ris alkyl); imines; hydrazones and substituted hydrazones (substituted,for example, with aromatic groups such as 2,4-dinitrophenyl); azines;semicarbazones; oximes; enamines; alkyldine bisamides (compounds havinga functional group having the structural formula --CH[NC(O)R₂ ]₂ whereR₂ is alkyl); alpha-aminoalkenesulfonic acids; cyanohydrins;1,3-oxazolidines; enol esters including enol acetates; and enol esters.Specific examples of latent aldehydes which generate hydrophilicaldehydes include aldehyde bisulfite addition product, and amino alkenesulfonic acids.

By alkylidene of an active methylene group is meant a functional grouphaving the structural formula

    --X--C(O)--C(Z)═CHR.sub.3

where X and Z are given above and R₃ is hydrogen or (C₁ -C₁₈)hydrocarboyl including (C₁ -C₁₈)alkyl, (C₇ -C₁₈)aralkyl, (C₂ -C₁₈)alkenyl, (C₇ -C₁₈)alkaryl, (C₈ -C₁₈)alkaralkyl, (C₈ -C₁₈) alkenaryl, (C₈-C₁₈)aralkenyl, and the like. Specific examples of hydrophilicbisalkylidenes of compounds having at least two

methylene groups per molecule includebis(isopropylidinecyanoacetyl)pentaerythritol, etc.

Examples of hydrophilic alpha, beta-ethylenically unsaturated carbonylcompounds include hydrophilic alpha, beta-ethylenically unsaturatedaldehydes such as acrolein and methacrolein. An example of a hydrophilicamine is phenylenediamine.

The temperature and pH of the continuous fluid phase are preferablyadjusted to promote reaction between the first and second reactivecompounds. This can be accomplished after the core particles have beendispersed within the continuous phase. For example, in the case of abase-catalyzed reaction, a solution of strong base can be added afterthe core particles are formed and the first and second reactivecompounds have been added to raise the pH of the reaction mixture. Theoptimum reaction conditions depend on the identity of the first andsecond reactive compounds.

In general, it is preferred that stoichiometric proportions of the firstand second reactive compounds be employed. The amount of first andsecond reactive compounds can be calculated from the particle size ofthe microcapsules to be formed, the desired shell thickness, and theamount of target material to be encapsulated. In general, the shellthickness will vary with the application for which the microcapsules areto be employed and the physical properties of the polymer formed by thereaction between the first and second reactive compounds. For example,rigid, impermeable relatively thin shells may be favored forapplications in which the microcapsules are to be ruptured by appliedpressure, such as in scent delivery and carbonless copy paperapplications, whereas relatively thick, relatively permeable low modulusshells may be favored for applications calling for sustained release ofthe target material.

The reaction between compounds containing at least one active methylenegroup and an aldehyde is well known in the organic chemical arts, and isknown as the Knovenagel condensation reaction. The Knovenagel reactionis reviewed in J. Jones, "The Knovenagel Condensation," OrganicReactions, Vol. 15 (A. C. Cope ed., John Wiley & Sons, New York 1967)204-582 and is summarized in J. March, Advanced Organic Chemistry (ThirdEdition, John Wiley & Sons, New York 1985) 835-841. When the activemethylene crosslinking agent is an alpha, beta-ethylenically unsaturatedcarbonyl compound, the reaction between the first and second reactivecompounds is known as the Michael addition reaction.

While it is presently believed that the shells of the microcapsules areformed by a polymerization reaction between the first and secondreactive compounds at or near the interface between the continuous anddispersed phases, the process of the present invention is not limited toinclude specific polymerization sites, and includes embodiments in whichpolymerization occurs in-situ in either the continuous or dispersedphase, with subsequent diffusion or migration of the polymeric materialto the interface between the phases.

If desired the first reactive compound can be chosen to be a compoundhaving at least two active methylene functional groups per molecule andthe second reactive compound can be chosen to be an activemethylene-reactive crosslinking agent. This embodiment of the presentprocess may be desirable when, for example, the target material itselfhas some reactivity with respect to the active methylene functionalgroups. For example, when the target material is a weakly reactivealdehyde, the present embodiment is preferred.

In the case in which the continuous fluid phase is hydrophilic, thesecond reactive compound can then be a hydrophilic compound having atleast two active methylene groups per molecule. For example, the secondreactive compound can be the reaction product of an ethoxylated orethoxylated/proxylated di- or polyol with a compound having thestructural formula

    H--X.sup.1 --C(O)--CH.sub.2 --Z

where Z is given above and X¹ is X above, excluding X═--O--(CH₂ CH₂)_(m)[CH(CH₃)CH₂ O]_(n). The ethoxylation and ethoxylation/propoxylation ofalcohols, including diols and polyols, is well known in the preparativechemical arts. See, for example, H. Greenwald et al., Surfactant ScienceSeries, Vol. I, Chapter 2, pp. 8-43, Ed. Martin J. Schick, MarcelDekker, Inc., N.Y., N.Y. Examples of diols and polyols which can be usedare given above. Specific examples of hydrophilic compounds having atleast two active methylene functional groups include tris[cyanoacetyl-(ethoxy)₅ ]glycerol, tris[cyanoacetyl(ethoxy)₆ ]trimethylolpropane,tris[nitroacetyl(ethoxy)₅ ]glycerol, di[cyanoacetyl(ethoxy)₇]trimethylolpropane, and tetra[acetoacetyl(ethoxy)₅ ]pentaerythritol.

When the second reactive compound is a hydrophilic compound having atleast two active methylene groups per molecule, the first reactivecompound is preferred to be a hydrophobic active methylene-reactivecrosslinking agent. Examples of hydrophobic active methylene-reactivecrosslinking agents include hydrophobic aldehydes, latent aldehydesgiving hydrophobic aldehydes, hydrophobic alkylidenes of compoundshaving at least two active methylene groups per molecule, hydrophobicalpha, beta-ethylenically unsaturated carbonyl compounds, andhydrophobic amines. Specific examples of hydrophobic aldehydes includen-octyl aldehyde, n-nonyl aldehyde, n-decylaldehyde, lauryl aldehyde,n-heptaldehyde, and stearaldehyde. Specific examples of latent aldehydesgiving hydrophobic aldehydes include n-octylaldehyde cyanohydrin, thephenylhydrazone of n-nonylaldehyde, and the ethanol acetal ofstearaldehyde. Examples of hydrophobic alkylidene compounds having atleast two active methylene groups per molecule includetris(isopropylidinecyanoacetyl)trimethylolpropane.

In addition to those previously described embodiments of the presentprocess in which the continuous fluid phase is hydrophilic and thedispersed core phase is hydrophobic, the present invention also includesembodiments in which a hydrophilic core phase is dispersed in ahydrophobic continuous fluid phase, such as water-in-oil emulsions.Thus, the present process can be used to encapsulate hydrophilic targetmaterials. In this embodiment of the process it is preferred that thecontinuous fluid phase be a hydrophobic fluid which is immiscible withwater and that the core phase, including the target material bewater-soluble. Examples of water-soluble target materials which can beencapsulated using this embodiment of the process include Kathon® 886 NWbiocide, salts of ethylenebisdithiocarbomate, such as Dithane® D-14fungicide, choline chloride, aldehydes such as formaldehyde, inorganicsalts such as zinc acetate, and free radical-generating compounds suchas ammonium persulfate.

The same techniques as described above for forming a hydrophobic corephase in a hydrophilic continuous fluid phase may in general be used todisperse a hydrophilic core phase in a hydrophobic continuous phase. Forexample, the hydrophilic core phase can be dispersed by gradually addingan aqueous solution containing a hydrophilic water-soluble targetmaterial, and a hydrophilic water-soluble first reactive compound, to ahydrophobic, substantially water-insoluble continuous fluid phase. As inthe case of the hydrophobic core phase dispersed in a hydrophiliccontinuous phase, the hydrophilic first reactive compound which isdispersed or dissolved in the hydrophilic core phase can be either acompound having at least two active methylene functional groups permolecule, or an active methylene-reactive crosslinking agent; it beingunderstood that the hydrophobic second reactive compound will then beeither an active methylene-reactive crosslinking agent or a compoundhaving at least two active methylene groups per molecule, respectively.

The hydrophobic continuous fluid phase can comprise an organic solvent,such as xylene, toluene, mineral spirits, or the like, or mixturesthereof.

If desired, conventional water-in-oil dispersants and/or stabilizers canbe employed. An example of a polymeric AND (nonaqueous dispersion)dispersing agent is a block copolymer having a polhydroxystearic blockand a polyacrylate block, the polyacrylate block being polymerized frommonomer including hydroxyethyl acrylate. Similarly, surface activeagents can be employed to stabilize the emulsion of hydrophilic coreparticles in the hydrophobic continuous phase, as is well known in theart. Examples of surface active agents which can be used to stabilizethe dispersed hydrophilic core phase in the continuous hydrophobic phaseinclude Span® (trademark of ICI Americas Inc.) 80 (sorbitan monooleate,HLB=4.3), and Triton® X-15 (trademark of Rohm and Haas Company)(t-octylphenol ethoxylate, HLB=3.6).

A dispersing agent such as a surface active agent can be used to aid indispersing the hydrophilic target material within the core particles andto aid in emulsifying and stabilizing the core particles. For example,the core phase can include conventional surface active agents such asthe dialkyl sulfosuccinates, for example, diethylhexyl sulfosuccinate,and Triton® X-400 (stearyldimethylbenzylammonium chloride).

After the polymeric shells have been formed around the core phaseparticles, the microcapsules can be separated from the continuous phaseby any process known in the physical separation arts, such as byfiltration, decantation, centrifugation, flash drying, spray drying,freeze drying, evaporation, distillation, and the like. The separationprocess selected is preferably chosen to effect a rapid and efficientseparation, with a minimum of mechanical damage to or disruption of themicrocapsules. In some cases, it may be desirable to use themicrocapsules dispersed in the continuous phase directly in anapplication, such as when the microcapsules are to be coated onto sheetstock or other surface. If desired, additional components can be addedto or dissolved in the continuous phase prior to use.

In one embodiment of the present process, the microcapsules containcrosslinking reagents for coating composition binders as targetmaterials, and the shells of the microcapsulves are selected to permitgradual release of the crosslinking reagent from the microcapsules afterthe coating composition has been applied to the surface to be coated.The microcapsules can contain a difunctional crosslinking reagent forthe coating composition binder, such as a diisocyanate or a diepoxide,and the capsule shell is formed to permit gradual release of thecrosslinking agent to crosslink the binder while the coating compositionis drying.

The following examples will aid those skilled in the art inunderstanding the process of the present invention, however, the presentinvention is in no way limited thereby. In the following examplesprecentage composition is by weight.

Example 1 - Microencapsulation of Hydrophobic Target Material Using aHydrophilic Crosslinking Agent

A continuous aqueous phase was prepared by mixing together 500 g of anaqueous solution of a six percent Vinol® (trademark of Air Products) 205polyvinyl alcohol, 625 g water, and 60 g of an aqueous solution of a onepercent diethylhexylsulfosuccinate. A hydrophobic solution phase wasprepared by mixing 80 g 1-pentanol, 320 g Skane® M-8 biocide(N-octylisothiazolone), 42 g dioctyl phthalate and 700 gtris(acetoacetyl)trimethylolpropane. The aqueous solution was added allat once to the hydrophobic solution and the mixture was homogenizedusing a Ross Homogenizer by stirring at 18,000 rpm for approximately tenminutes. The emulsified mixture was transferred to a 5 liter flask andthe emulsification vessel (a half-gallon jar) was rinsed with a mixtureof 250 g of six percent Vinol® 205 aqueous solution and 356 g of water,the rinse fluid being added to the flask. To the emulsified mixture wasadded gradually while stirring vigorously a mixture of 190 g of a 37%aqueous solution of formaldehyde and 416 g water. Next, a mixture of 7.2g of 50% sodium hydroxide and 72 g water was added to the reactionmixture. Stirring was continued for about sixty minutes, and theresulting dispersion of microcapsules in the aqueous continuous phasewas filtered through cheesecloth.

Example 2 - Microencapsulation of a Hydrophilic Target Material Using aHydrophilic Crosslinker

A continuous hydrophobic organic phase was prepared by mixing together174 g xylene, 174 g odorless mineral spirits, 6 g Span® 80 surfactant(sorbitan monooleate), 48 g of a block copolymer of polyhydroxystearicacid and polyhydroxyethylacrylate (35%) and 72 gtris(acetoacetyl)trimethylolpropane. An aqueous phase was prepared bymixing 180 g water, 180 g Kathon® 886 MW biocide, and 44.4 g of a sevenpercent aqueous solution of diethyl sulfosuccinate. The aqueous phasewas added all at once to the hydrophobic organic phase and the mixturewas homogenized using a Ross Homogenizer by stirring at about 18,000 rpmfor approximately five minutes. The homogenizer speed was reduced toabout 5,000 rpm and 45 g of a two percent aqueous solution of sodiumhydroxide was added to the homogenized mixture. After an additional 2-3minutes 23.2 g of a seven percent aqueous solution of formaldehyde wasadded to the homogenized mixture and stirring was continued for severaladditional minutes in the homogenizer. Next, the homogenized mixture wastransferred to a flask and was stirred with a mechanical stirrer forabout 15-20 minutes. Finally, the dispersion of microcapsules in thecontinuous organic phase was filtered through cheesecloth.

During the homogenization step the temperature of the mixture increases,the temperature increase being a function of volume. With moderatevolumes (about one liter) temperatures of up to about 45° C. areobserved. Before adding base and crosslinker, the mixture is preferablycooled to room temperature using cold water.

Example 3 - Microencapsulation of a Hydrophobic Target Compound Using aHydrophobic Crosslinker

A continuous aqueous phase was prepared by mixing together 16.7 g of sixpercent aqueous solution of Vinol® 205 polyvinylalcohol, 21.7 g water, 3g of a one percent aqueous solution of diethylsulfosuccinate, and 20.6 gof tris[cyanoacetyl(ethoxy)5]glycerol. A hydrophobic organic phasesolution was prepared by mixing together 6 g 1-pentanol, 1.4 g dioctylphthalate, 5 g toluene, 4.3 g n-octyl aldehyde, and 0.6 g Skane® M-8mildicide. The aqueous phase was added to the organic phase andhomogenized at about 18,000 rpm using a Ross Homogenizer forapproximately 10 minutes. The homogenizer speed was reduced toapproximate 1,800 rpm and 2.2 g of a two percent aqueous solution ofsodium hydroxide was added. After 2-3 minutes, the homogenized mixturewas transferred to a magnetic stir plate and stirring was continued for20 minutes, and the microcapsule containing dispersion was filteredthrough cheesecloth.

Example 4 - Microencapsulation of a Hydrophilic Target Compound Using aHydrophobic Crosslinker

A continuous hydrophobic organic phase was prepared by mixing together0.5 g sorbitan monooleate, 14.5 g xylene, 14.5 g odorless mineralspirits, 4.0 g 35% solution of a block copolymer of polyhydroxystearicacid and polyhydroxyethylacrylate, and 2.2 g octyl aldehyde. An aqueousphase was prepared by mixing together 3.7 g of a seven percent solutionof diethylsulfosuccinate, 7.5 g water, 15 g of Kathon® 886 MW bio 10.3 gtris[cyanoacetyl(ethoxy)5] glycerol. The aqueous phase was added to thehydrophobic phase and homogenized at about 18,000 rpm in a RossHomogenizer for approximately five minutes. The homogenizer speed wasreduced to about 5,000 rpm and 1.1 g of a two percent aqueous solutionof sodium hydroxide was added. After 2-3 minutes the homogenized mixturewas transferred to a magnetic stir plate and stirred for 15-20 minutes.The microcapsule containing dispersion was filtered through cheesecloth.

Example 5 - Crosslinking A Coating Composition Binder UsingMicroencapsulated Epoxy

A dispersion of encapsulated Epon® (trademark of Shell) 830 resin(diepoxide of bisphenol A) is prepared according to Example 1 above. Thedispersion is prepared to contain 50 milliequivalents of epoxy per 100 gdispersion. The dispersion is blended with an amine-functional coatingbinder resin containing 52 milliequivalents amine per 100 g resin.Therefore, 100 g dispersion are to be blended with 96 g resin, and afilm is to be cast from the blend. When dried and cured at roomtemperature, the film will be found to be swellable but insoluble in asolvent for the amine resin, such as acetone. The blend will show agradual viscosity increase over several weeks, while a control blend ofEpon® 830 resin and the aminefunctional resin will gel within a day orso. Said amine functional resin could be utilized in applications suchas adhesives, binders, caulks, coatings, mastics, etc.

Using substantially the same processes as given in Examples 1 and 2above, the following additional examples of microencapsulated targetmaterials were prepared according to the present invention:

    ______________________________________                                        Ex-  Active                                                                   am-  Methyl-  Cross-       Target    Cont.                                    ple  ene      linker       Material  Phase                                    ______________________________________                                         6   A.sup.1  HCHO         butyl acetate                                                                           Aq                                                                            (Aqueous)                                 7   A.sup.1  HCHO         S-150.sup.10                                                                            Aq                                        8   A.sup.1  HCHO         Skane ®.sup.14                                                                      Aq                                        9   A.sup.1  HCHO         S-150     Aq                                       10   A.sup.1  HCHO         Skane ®                                                                             Aq                                       11   A.sup.1  HCHO         Skane ®                                                                             Aq                                       12   A.sup.1  HCHO         water     Or                                                                            (Organic)                                13   A.sup.1  HCHO         Kathon ®.sup.11                                                                     Or                                       14   A.sup.1  HCHO         Dithane ®.sup.12                                                                    Or                                       15   A.sup.1  HCHO         Kathon ®                                                                            Or                                       16   A.sup.1  HCHO         water     Or                                       17   A.sup.1  HCHO         choline   Or                                       18   A.sup.1  HCHO         Skane ®                                                                             Aq                                       19   A.sup.1  HCHO         Skane ®                                                                             Aq                                       20   A.sup.1  HCHO         Karathane ®.sup.13                                                                  Aq                                       21   A.sup.1  HCHO         Kathon ®                                                                            Or                                       22   B.sup.2  HCHO         Skane ®                                                                             Aq                                       23   C.sup.3  HCHO         Skane ®                                                                             Aq                                       24   A        HCHO         ammonium  Or                                                                  persulfate                                         25   A        glyoxal      Skane ®                                                                             Aq                                       26   A        acrolein     Skane  ®                                                                            Aq                                       27   A        glutaraldehyde                                                                             Skane ®                                                                             Aq                                       28   A        furfural     Skane ®                                                                             Aq                                       29   A        HCHO         Kathon ®                                                                            Or                                       30   A        HCHO         choline   Or                                       31   B        HCHO         Kathon ®                                                                            Or                                       32   C        HCHO         Kathon ®                                                                            Or                                       33   A        acrolein     Kathon ®                                                                            Or                                       34   A        glutaraldehyde                                                                             Kathon ®                                                                            Or                                       35   A        HCHO         ammonium  Or                                                                  persulfate                                         36   A        glyoxal      Kathon ®                                                                            Or                                       37   A        HCHO         phenolphthalein                                                                         Or                                       38   A        HCHO         Skane ®                                                                             Aq                                       39   A        HCHO         HCHO      Or                                       40   A        HCHO         zinc acetate                                                                            Or                                       41   A        acrolein     toluene   Aq                                       42   A        methacrolein toluene   Aq                                       43   A        propionaldehyde                                                                            toluene   Aq                                       44   A        phenylenediamine                                                                           Skane ®                                                                             Aq                                       45   A        HCHO         Skane ®                                                                             Aq                                       46   D.sup.4 /A                                                                             HCHO         Skane ®                                                                             Aq                                       47   A        glucose      Skane ®                                                                             Aq                                       48   E.sup.5  HCHO         Skane ®                                                                             Aq                                       49   A        HCHO         Kathon ®                                                                            Or                                       50   D/A      HCHO         Kathon ®                                                                            Or                                       51   A        glucose      Kathon ®                                                                            Or                                       52   E        HCHO         Kathon ®                                                                            Or                                       53   A        HCHO         Skane ®                                                                             Aq                                       54   A        HCHO         Desmodur ®                                                                          Aq                                                                  W.sup.16                                           55   A        HCHO         Epon 830.sup.17                                                                         Aq                                       56   A        HCHO         toluene   Aq                                       57   F.sup.6  HCHO         toluene   Aq                                       58   F        HCHO         Skane ®                                                                             Aq                                       59   G.sup.7  HCHO         toluene   Aq                                       60   G        HCHO         Skane ®                                                                             Aq                                       61   H.sup.8 /A                                                                             HCHO         toluene   Aq                                       62   H/A      HCHO         Skane ®                                                                             Aq                                       63   A        HCHO         saline    Or                                       64   H/A      HCHO         Kathon ®                                                                            Or                                       65   H/A      HCHO         saline    Or                                       66   F        HCHO         Kathon ®                                                                            Or                                       67   F        HCHO         saline    Or                                       68   G        HCHO         Kathon ®                                                                            Or                                       69   G        HCHO         saline    Or                                       70   A        HCHO         Kathon ®                                                                            Or                                       71   A        HCHO         Desmodur ® W                                                                        Aq                                       72   A        HCHO         Goal ®.sup.15                                                                       Aq                                       73   F        HCHO         Goal ®.sup.15                                                                       Aq                                       74   G        HCHO         Goal ®.sup.15                                                                       Aq                                       75   A        HCHO         Skane ®                                                                             Aq                                       76   I.sup.9  HCHO         toluene   Aq                                       77   I        HCHO         Skane ®                                                                             Aq                                       78   I        HCHO         Kathon ® 886                                                                        Or                                       79   I        HCHO         saline    Or                                       ______________________________________                                         .sup.1 A = tris(acetoacetyl)trimethylolpropane                                .sup.2 B = tris(cyanoacetyl)trimethylolpropane                                .sup.3 C = tris(nitroacetoacetyl)trimethylolpropane                           .sup.4 D = bis(Nmethyl-N-hydroxyethylcyanoacetamido)adipate D/A is            18.2/11.7 by weight, but is 1/1 by acetoacetate equivalent                    .sup.5 E = tris(isopropylidinecyanoacetyl)trimethylolpropane                  .sup.6 F = tetra(acetoacetyl)pentaerythritol                                  .sup.7 G = tetra(acetoacetyl)erythritol                                       .sup.8 H = bis(acetoacetyl)bisphenol A H/A is 22.9/11.7 by weight, but is     1/1 by acetoacetate equivalent                                                .sup.9 I = tris(cyanoacetyl)glycerol                                          .sup.10 S150 (Solvesso 150) is now called Aromatic 150, Exxon. It is an       alkylbenzene solvent, a mixture of C.sub.9 -C.sub.12, mostly C.sub.10,        with a 50% distillation point at 193 C.                                       .sup.11 "Kathon ®" is Nmethyl-5-chloroisothiazolone                       .sup.12 "Dithane ®" D14 is disodium ethylene1,2-bisdithiocarbamate        (nabam)                                                                       .sup.13 "Karathane ®" is dinitrooctylphenylcrotonates (dinocap)           .sup.14 "Skane ® is Noctyl isothiazolone                                  .sup.15 "Goal ®" is oxyfluorfen                                           .sup.16 "Desmodur ® W" is bis(4,4diisocyanocyclohexyl) methane            .sup.17 "Epon ® 830" is a diepoxide of bisphenol                     

Using substantially the same processes as given in Examples 3 and 4above, the following additional examples of microencapsulated targetmaterials were prepared:

    ______________________________________                                                Active    Cross-    Target   Cont.                                    Example Methylene linker    Material Phase                                    ______________________________________                                        80      B         acetone   Skane ®                                                                            Aq                                                                            (Aqueous)                                81      B         acetone   toluene  Aq                                       82      J.sup.1   octyl     Skane ®                                                                            Aq                                                         aldehyde                                                    83      J         octyl     toluene  Aq                                                         aldehyde                                                    84      J         octyl     Kathon ® 886                                                                       Or                                                         aldehyde           (Organic)                                85      J         octyl     saline   Or                                       aldehyde                                                                      ______________________________________                                         .sup.1 J = tris[cyanoacetyl(ethoxy).sub.5 ]glycerol                      

Usual methods of determining the release rate of target compounds fromformulated materials, e.g. drugs or agricultural chemicals, iscomplicated in the present case because of the colloidal nature of theproducts of the present process. This requires the separation of thereleased compound from the unreleased formulated compound. For thisreason we have developed a release measuring system in which thecompound is released from the formulation and then separated viadiffusion through a set of hollow fiber dialysis membranes. Since a partof this system is just the diffusion of the free compound through thehollow fibers, all release measurements are compared to a control ofunformulated compound, thus a relative release rate is determined.Further, by comparing all runs to a control, any differences betweenhollow fiber sets are normalized.

In order to make the measurement, a constant level of target material isdispersed into a set weight of water. A hollow fiber set, in the shapeof a U is placed into the dispersion including the target material.Water is pumped through the hollow fibers, at a specific rate, into areservoir with a preset weight of water. The target material diffusesfrom inside the microcapsules into the disperse aqueous phase, and thenthrough the hollow fiber membrane into the reservoir system. Theaccumulation of the target material in the reservoir system is monitoredby sampling the reservoir at various times throughout the run.

Various modifications can be made in the details of the variousembodiments of the process of the present invention, all within thespirit and scope of the invention as defined in the appended claims.

We claim:
 1. A process for encapsulating a target material in adispersion of insoluble core-shell particles dispersed in a continuousfluid phase, the process comprising;(a) preparing a core emulsionincluding a core phase of unpolymerized discrete core particlesdispersed in said continuous fluid phase by emulsifying in saidcontinuous fluid phase a mixture comprising;(1) a target material, (2) adispersant for said core particles in said continuous fluid phase; (b)combining with said target material an unpolymerized first reactivecompound insoluble in said continuous fluid phase, said first reactivecompound being one of the compounds selected from the group consistingof(1) compounds having at least two active methylene functional groupsper molecule, and; (2) active methylene-reactive crosslinking agents;(c) combining with said continuous fluid phase an unpolymerized secondreactive compound which is soluble or dispersible in said continuousfluid phase and is one of the compounds selected from the groupconsisting of(1) compounds having at least two active methylenefunctional groups per molecule, and; (2) active methylene-reactivecrosslinking agents; wherein said second reactive compound is reactivewith said first reactive compound; and (d) reacting said first reactivecompound with said second reactive compound to form polymericencapsulating shells around said core particles.
 2. A process accordingto claim 1 further including adding a catalytic amount of base to saidcontinuous phase.
 3. A process according to claim 1 wherein saidcontinuous fluid phase includes water and said core phase and targetmaterial are hydrophobic.
 4. A process according to claim 3 wherein saidcore emulsion further includes an emulsion stabilizer.
 5. A processaccording to claim 3 wherein said dispersant is a polyvinyl alcohol. 6.A process according to claim 1 wherein said continuous fluid phase is ahydrophobic fluid immiscible with water and wherein said core phase andsaid target material are water-soluble.
 7. A process according to claim6 wherein said dispersant is polymeric and includes a polyhydroxystearicacid block and a polyacrylate block, wherein said polyacrylate block ispolymerized from monomer including hydroxyethyl acrylate.
 8. A processaccording to claim 1 wherein said compounds having at least two activemethylene functional groups per molecule are compounds having two ormore functional groups having the structure;

    --X--C(O)--CH.sub.2 --Z

wherein X is selected from the group consisting of --NR--, --O--, --S--,--O(CH₂ CH₂ O)_(m) [CH--(CH₃ CH₂ O]_(n) --, and --N(CH₂ CH₂ O)_(m)[CH(CH₃)CH₂ O]_(n) --, and m, n=0-4, independently, and wherein Z isselected from the group consisting of --C(O)R, --CO₂ H, --CO₂ R,--C(O)NHR, --C(O)NR₂, --CN, --NO₂, --SOR, --SO₂ R, --SO₃ R, phenyl, and(C₁ -C₃) alkyl substituted phenyl, and wherein R is (C₁ -C₆) alkyl.
 9. Aprocess according to claim 1 wherein said active methylene-reactivecrosslinking agents are selected from the group consisting of aldehydes,latent aldehydes, and the alkylidenes of compounds having at least twoactive methylene functional groups.
 10. A process according to claim 9wherein said latent aldehydes are selected from the group consistingof(a) acetals (b) hemiacetals (c) adducts of an aldehyde and bisulfite,the adduct having a functional group having the formula;

    --C(OH)SO.sup.- M.sup.+

wherein M is an alkali metal, (d) adducts of an aldehyde and ammonia,(e) adducts of an aldehyde and an amine, (f) imines, (g) hydrazones, (h)substituted hydrazones, (i) azines, (j) semicarbazones, (k) oximes, (l)alkyldine bisamides, (m) alpha-aminoalkanesulfonic acids, (n)cyanohydrins, (o) 1,3-oxazolidines, (p) enol esters, and (q) enol ethers11. A process according to claim 9 wherein said latent aldehydes areselected from the group consisting of hexamethylenetetraamine andhexahydro-2,4,6-trimethyl-1,3,5-triazine.
 12. A process according toclaim 9 wherein said alkylidenes are compounds having at least twoalkylidene functional groups, each alkylidene functional group havingthe formula

    --X--C(O)--C(Z)═CHR.sub.1

wherein R₁ is H or (C₁ -C₁₈) alkyl, wherein X is --NR--, --O--, --S--,--O (CH₂ CH₂ O) _(m) [CH--(CH₃)CH₂ O]_(n) --, or --N(CH₂ CH₂ O) _(m)[CH(CH₃)CH₂ O]_(n) --, and m, n=0-4, independently, and wherein Z is--C(O)R, --CO₂ H, --CO₂ R, --C(O)NHR, --C(O)NR₂, --CN, --NO₂, --SOR,--SO₂ R, --SO₃ R, phenyl, or (C₁ -C₃) alkyl substituted phenyl.
 13. Aprocess according to claim 1 wherein said first reactive compound andsaid second reactive compound react at the interface between saidcontinuous fluid phase and said core phase of discrete core particles toform said polymeric encapsulating shells.
 14. A process according toclaim 1 wherein said core phase is dispersed in said continuous fluidphase by emulsifying said phases at high shear.
 15. A process accordingto claim 1 wherein said first reactive compound is a triester oftrimethylolpropane and a carboxylic acid having an active methylenefunctional group.
 16. A process according to claim 15 wherein saidcarboxylic acid is selected from the group consisting of acetoaceticacid, cyanoacetic acid, and nitroacetic acid.
 17. A process according toclaim 1 wherein said second reactive compound is selected from the groupconsisting of formaldehyde, glyoxal, glutaraldehyde, and acrolein.
 18. Aprocess according to claim 1 wherein said target material is apesticide.
 19. A process according to claim 1 wherein said targetmaterial is a mildicide.
 20. A process according to claim 1 wherein saidtarget material is a pharmaceutical.
 21. A process according to claim 1wherein said target material is a crosslinking agent for polymericfilms.
 22. A process according to claim 21 wherein said crosslinkingagent is selected from the group consisting of diisocyanates andpolyisocyanates.
 23. A process according to claim 1 wherein said targetmaterial is a colorless dye precursor.
 24. Core-shell particlescontaining encapsulated target material within walls of condensationpolymer product prepared according to the process of claim 1 saidcore-shell particles having a diameter on the order of 0.5 micron andless.